Adhesives based on ethylene-propylene rubber copolymer (EPR) and/or an ethylene-propylene diene monomer rubber terpolymer (EPDM) are known in the art.
U.S. Pat. No. 5,798,175 discloses pressure sensitive adhesive (PSA) compositions based on a natural rubber or synthetic rubber and an amorphous polyolefin blend comprising EPR, hydrogenated polyisoprene and atactic polypropylene (APP). The adhesives are prepared by compounding the above-mentioned polymers, a compatible tackifier and an organic solvent. The adhesives are thus solvent based and not hot melts.
U.S. Pat. No. 5,612,144 discloses an adhesive tape composition comprising a polymer blend of at least one EPDM rubber, or preferably three different grades of EPDM rubbers in equal amounts, and another polymer selected from polyisoprene, polybutadiene, EPR, and mixtures thereof.
U.S. Pat. No. 5,618,883 discloses a hot melt pressure sensitive adhesive composition comprising a tackified EPR rubber modified with a copolymer of styrene-ethylene-butylene-styrene block copolymer and/or styrene-ethylene-propylene-styrene block copolymer.
These prior art compositions rely on curing or chemical crosslinking to acquire good cohesive strength and good adhesion characteristics.
U.S. Pat. No. 6,143,818 discloses a hot melt adhesive composition, comprising a polymer component consisting of EPR and/or EPDM rubber and at least one semi-crystalline olefinic polymer. The compositions provide an excellent heat stability, and good adhesion to a variety of substrates. Nevertheless the viscosity of the polymer component is too high for a number of applications, especially for those applications where a low viscosity of the adhesive or a high polymer proportion in the adhesive formulation is strongly required.
Notwithstanding the state of technology, it would be desirable to provide adhesives based on EPR and/or EPDM rubbers and semi-crystalline olefinic polymers, which exhibit a high cohesive strength, a narrow molecular weight distribution coupled with a low melt viscosity and a high flexibility.